/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.shrink;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.annotation.visitor.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.constant.*;
import proguard.classfile.editor.*;
import proguard.classfile.util.*;
import proguard.classfile.visitor.*;

import java.util.*;

import a.annotation.proguard.classfile.attribute.annotation.*;

/**
 * This ClassVisitor removes constant pool entries, class members, and other class elements that are not marked as being
 * used.
 *
 * @author Eric Lafortune
 */
public class ClassShrinker extends SimplifiedVisitor
    implements ClassVisitor, MemberVisitor, AttributeVisitor, AnnotationVisitor, ElementValueVisitor {
    private final UsageMarker usageMarker;

    private int[] constantIndexMap = new int[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
    private int[] bootstrapMethodIndexMap = new int[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
    private final ConstantPoolRemapper constantPoolRemapper = new ConstantPoolRemapper();
    private final BootstrapMethodRemapper bootstrapMethodRemapper = new BootstrapMethodRemapper();

    /**
     * Creates a new ClassShrinker.
     * 
     * @param usageMarker the usage marker that is used to mark the classes and class members.
     */
    public ClassShrinker(UsageMarker usageMarker) {
        this.usageMarker = usageMarker;
    }

    // Implementations for ClassVisitor.

    public void visitProgramClass(ProgramClass programClass) {
        // Shrink the arrays for constant pool, interfaces, fields, methods,
        // and class attributes.
        if (programClass.u2interfacesCount > 0) {
            new InterfaceDeleter(
                shrinkFlags(programClass.constantPool, programClass.u2interfaces, programClass.u2interfacesCount))
                    .visitProgramClass(programClass);
        }

        // Shrinking the constant pool also sets up an index map.
        int newConstantPoolCount = shrinkConstantPool(programClass.constantPool, programClass.u2constantPoolCount);

        int oldFieldsCount = programClass.u2fieldsCount;
        programClass.u2fieldsCount = shrinkArray(programClass.fields, programClass.u2fieldsCount);
        if (programClass.u2fieldsCount < oldFieldsCount) {
            programClass.u2accessFlags |= ClassConstants.ACC_REMOVED_FIELDS;
        }

        int oldMethodsCount = programClass.u2methodsCount;
        programClass.u2methodsCount = shrinkArray(programClass.methods, programClass.u2methodsCount);
        if (programClass.u2methodsCount < oldMethodsCount) {
            programClass.u2accessFlags |= ClassConstants.ACC_REMOVED_METHODS;
        }

        programClass.u2attributesCount = shrinkArray(programClass.attributes, programClass.u2attributesCount);

        // Compact the remaining fields, methods, and attributes,
        // and remap their references to the constant pool.
        programClass.fieldsAccept(this);
        programClass.methodsAccept(this);
        programClass.attributesAccept(this);

        // Remap the references to the constant pool if it has shrunk.
        if (newConstantPoolCount < programClass.u2constantPoolCount) {
            programClass.u2constantPoolCount = newConstantPoolCount;

            // Remap all constant pool references.
            constantPoolRemapper.setConstantIndexMap(constantIndexMap);
            constantPoolRemapper.visitProgramClass(programClass);
        }

        // Replace any unused classes in the signatures.
        MySignatureCleaner signatureCleaner = new MySignatureCleaner();
        programClass.fieldsAccept(new AllAttributeVisitor(signatureCleaner));
        programClass.methodsAccept(new AllAttributeVisitor(signatureCleaner));
        programClass.attributesAccept(signatureCleaner);

        // Compact the extra field pointing to the subclasses of this class.
        programClass.subClasses = shrinkToNewArray(programClass.subClasses);
    }

    public void visitLibraryClass(LibraryClass libraryClass) {
        // Library classes are left unchanged.

        // Compact the extra field pointing to the subclasses of this class.
        libraryClass.subClasses = shrinkToNewArray(libraryClass.subClasses);
    }

    // Implementations for MemberVisitor.

    public void visitProgramMember(ProgramClass programClass, ProgramMember programMember) {
        // Shrink the attributes array.
        programMember.u2attributesCount = shrinkArray(programMember.attributes, programMember.u2attributesCount);

        // Shrink any attributes.
        programMember.attributesAccept(programClass, this);
    }

    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

    public void visitBootstrapMethodsAttribute(Clazz clazz, BootstrapMethodsAttribute bootstrapMethodsAttribute) {
        // Shrink the array of BootstrapMethodInfo objects.
        int newBootstrapMethodsCount = shrinkBootstrapMethodArray(bootstrapMethodsAttribute.bootstrapMethods,
            bootstrapMethodsAttribute.u2bootstrapMethodsCount);

        if (newBootstrapMethodsCount < bootstrapMethodsAttribute.u2bootstrapMethodsCount) {
            bootstrapMethodsAttribute.u2bootstrapMethodsCount = newBootstrapMethodsCount;

            // Remap all bootstrap method references.
            bootstrapMethodRemapper.setBootstrapMethodIndexMap(bootstrapMethodIndexMap);
            clazz.constantPoolEntriesAccept(bootstrapMethodRemapper);
        }
    }

    public void visitInnerClassesAttribute(Clazz clazz, InnerClassesAttribute innerClassesAttribute) {
        // Shrink the array of InnerClassesInfo objects.
        innerClassesAttribute.u2classesCount =
            shrinkArray(innerClassesAttribute.classes, innerClassesAttribute.u2classesCount);
    }

    public void visitEnclosingMethodAttribute(Clazz clazz, EnclosingMethodAttribute enclosingMethodAttribute) {
        // Sometimes, a class is still referenced (apparently as a dummy class),
        // but its enclosing method is not. Then remove the reference to
        // the enclosing method.
        // E.g. the anonymous inner class javax.swing.JList$1 is defined inside
        // a constructor of javax.swing.JList, but it is also referenced as a
        // dummy argument in a constructor of javax.swing.JList$ListSelectionHandler.
        if (enclosingMethodAttribute.referencedMethod != null
            && !usageMarker.isUsed(enclosingMethodAttribute.referencedMethod)) {
            enclosingMethodAttribute.u2nameAndTypeIndex = 0;

            enclosingMethodAttribute.referencedMethod = null;
        }
    }

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        // Shrink the attributes array.
        codeAttribute.u2attributesCount = shrinkArray(codeAttribute.attributes, codeAttribute.u2attributesCount);

        // Shrink the attributes themselves.
        codeAttribute.attributesAccept(clazz, method, this);
    }

    public void visitLocalVariableTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute,
        LocalVariableTableAttribute localVariableTableAttribute) {
        // Shrink the local variable info array.
        localVariableTableAttribute.u2localVariableTableLength = shrinkArray(
            localVariableTableAttribute.localVariableTable, localVariableTableAttribute.u2localVariableTableLength);
    }

    public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute,
        LocalVariableTypeTableAttribute localVariableTypeTableAttribute) {
        // Shrink the local variable type info array.
        localVariableTypeTableAttribute.u2localVariableTypeTableLength =
            shrinkArray(localVariableTypeTableAttribute.localVariableTypeTable,
                localVariableTypeTableAttribute.u2localVariableTypeTableLength);
    }

    public void visitAnyAnnotationsAttribute(Clazz clazz, AnnotationsAttribute annotationsAttribute) {
        // Shrink the annotations array.
        annotationsAttribute.u2annotationsCount =
            shrinkArray(annotationsAttribute.annotations, annotationsAttribute.u2annotationsCount);

        // Shrink the annotations themselves.
        annotationsAttribute.annotationsAccept(clazz, this);
    }

    public void visitAnyParameterAnnotationsAttribute(Clazz clazz, Method method,
        ParameterAnnotationsAttribute parameterAnnotationsAttribute) {
        // Loop over all parameters.
        for (int parameterIndex = 0; parameterIndex < parameterAnnotationsAttribute.u1parametersCount;
            parameterIndex++) {
            // Shrink the parameter annotations array.
            parameterAnnotationsAttribute.u2parameterAnnotationsCount[parameterIndex] =
                shrinkArray(parameterAnnotationsAttribute.parameterAnnotations[parameterIndex],
                    parameterAnnotationsAttribute.u2parameterAnnotationsCount[parameterIndex]);
        }

        // Shrink the annotations themselves.
        parameterAnnotationsAttribute.annotationsAccept(clazz, method, this);
    }

    // Implementations for AnnotationVisitor.

    public void visitAnnotation(Clazz clazz, Annotation annotation) {
        // Shrink the element values array.
        annotation.u2elementValuesCount = shrinkArray(annotation.elementValues, annotation.u2elementValuesCount);

        // Shrink the element values themselves.
        annotation.elementValuesAccept(clazz, this);
    }

    /**
     * This AttributeVisitor updates the Utf8 constants of signatures of classes, fields, and methods.
     */
    private class MySignatureCleaner extends SimplifiedVisitor implements AttributeVisitor {
        public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

        public void visitSignatureAttribute(Clazz clazz, SignatureAttribute signatureAttribute) {
            Clazz[] referencedClasses = signatureAttribute.referencedClasses;
            if (referencedClasses != null) {
                // Go over the classes in the signature.
                String signature = signatureAttribute.getSignature(clazz);

                DescriptorClassEnumeration classEnumeration = new DescriptorClassEnumeration(signature);

                int referencedClassIndex = 0;

                // Start construction a new signature.
                StringBuffer newSignatureBuffer = new StringBuffer();

                newSignatureBuffer.append(classEnumeration.nextFluff());

                while (classEnumeration.hasMoreClassNames()) {
                    String className = classEnumeration.nextClassName();

                    // Replace the class name if it is unused.
                    Clazz referencedClass = referencedClasses[referencedClassIndex];
                    if (referencedClass != null && !usageMarker.isUsed(referencedClass)) {
                        className = ClassConstants.NAME_JAVA_LANG_OBJECT;

                        referencedClasses[referencedClassIndex] = null;
                    }

                    // Use a short name if it's an inner class after a '.'
                    // separator.
                    else if (classEnumeration.isInnerClassName()) {
                        className =
                            className.substring(className.lastIndexOf(ClassConstants.INNER_CLASS_SEPARATOR) + 1);
                    }

                    referencedClassIndex++;

                    newSignatureBuffer.append(className);
                    newSignatureBuffer.append(classEnumeration.nextFluff());
                }

                // Update the signature.
                ((Utf8Constant)((ProgramClass)clazz).constantPool[signatureAttribute.u2signatureIndex])
                    .setString(newSignatureBuffer.toString());
            }
        }
    }

    // Implementations for ElementValueVisitor.

    public void visitAnyElementValue(Clazz clazz, Annotation annotation, ElementValue elementValue) {}

    public void visitAnnotationElementValue(Clazz clazz, Annotation annotation,
        AnnotationElementValue annotationElementValue) {
        // Shrink the contained annotation.
        annotationElementValue.annotationAccept(clazz, this);
    }

    public void visitArrayElementValue(Clazz clazz, Annotation annotation, ArrayElementValue arrayElementValue) {
        // Shrink the element values array.
        arrayElementValue.u2elementValuesCount =
            shrinkArray(arrayElementValue.elementValues, arrayElementValue.u2elementValuesCount);

        // Shrink the element values themselves.
        arrayElementValue.elementValuesAccept(clazz, annotation, this);
    }

    // Small utility methods.

    /**
     * Removes all entries that are not marked as being used from the given constant pool. Creates a map from the old
     * indices to the new indices as a side effect.
     * 
     * @return the new number of entries.
     */
    private int shrinkConstantPool(Constant[] constantPool, int length) {
        if (constantIndexMap.length < length) {
            constantIndexMap = new int[length];
        }

        int counter = 1;
        boolean isUsed = false;

        // Shift the used constant pool entries together.
        for (int index = 1; index < length; index++) {
            constantIndexMap[index] = counter;

            Constant constant = constantPool[index];

            // Is the constant being used? Don't update the flag if this is the
            // second half of a long entry.
            if (constant != null) {
                isUsed = usageMarker.isUsed(constant);
            }

            if (isUsed) {
                // Remember the new index.
                constantIndexMap[index] = counter;

                // Shift the constant pool entry.
                constantPool[counter++] = constant;
            } else {
                // Remember an invalid index.
                constantIndexMap[index] = -1;
            }
        }

        // Clear the remaining constant pool elements.
        Arrays.fill(constantPool, counter, length, null);

        return counter;
    }

    /**
     * Creates an array marking unused constant pool entries for all the elements in the given array of constant pool
     * indices.
     * 
     * @return an array of flags indicating unused elements.
     */
    private boolean[] shrinkFlags(Constant[] constantPool, int[] array, int length) {
        boolean[] unused = new boolean[length];

        // Remember the unused constants.
        for (int index = 0; index < length; index++) {
            if (!usageMarker.isUsed(constantPool[array[index]])) {
                unused[index] = true;
            }
        }

        return unused;
    }

    /**
     * Removes all indices that point to unused constant pool entries from the given array.
     * 
     * @return the new number of indices.
     */
    private int shrinkConstantIndexArray(Constant[] constantPool, int[] array, int length) {
        int counter = 0;

        // Shift the used objects together.
        for (int index = 0; index < length; index++) {
            if (usageMarker.isUsed(constantPool[array[index]])) {
                array[counter++] = array[index];
            }
        }

        // Clear the remaining array elements.
        Arrays.fill(array, counter, length, 0);

        return counter;
    }

    /**
     * Removes all Clazz objects that are not marked as being used from the given array and returns the remaining
     * objects in a an array of the right size.
     * 
     * @return the new array.
     */
    private Clazz[] shrinkToNewArray(Clazz[] array) {
        if (array == null) {
            return null;
        }

        // Shrink the given array in-place.
        int length = shrinkArray(array, array.length);
        if (length == 0) {
            return null;
        }

        // Return immediately if the array is of right size already.
        if (length == array.length) {
            return array;
        }

        // Copy the remaining elements into a new array of the right size.
        Clazz[] newArray = new Clazz[length];
        System.arraycopy(array, 0, newArray, 0, length);
        return newArray;
    }

    /**
     * Removes all entries that are not marked as being used from the given array of bootstrap methods. Creates a map
     * from the old indices to the new indices as a side effect.
     * 
     * @return the new number of entries.
     */
    private int shrinkBootstrapMethodArray(BootstrapMethodInfo[] bootstrapMethods, int length) {
        if (bootstrapMethodIndexMap.length < length) {
            bootstrapMethodIndexMap = new int[length];
        }

        int counter = 0;

        // Shift the used bootstrap methods together.
        for (int index = 0; index < length; index++) {
            BootstrapMethodInfo bootstrapMethod = bootstrapMethods[index];

            // Is the entry being used?
            if (usageMarker.isUsed(bootstrapMethod)) {
                // Remember the new index.
                bootstrapMethodIndexMap[index] = counter;

                // Shift the entry.
                bootstrapMethods[counter++] = bootstrapMethod;
            } else {
                // Remember an invalid index.
                bootstrapMethodIndexMap[index] = -1;
            }
        }

        // Clear the remaining bootstrap methods.
        Arrays.fill(bootstrapMethods, counter, length, null);

        return counter;
    }

    /**
     * Removes all VisitorAccepter objects that are not marked as being used from the given array.
     * 
     * @return the new number of VisitorAccepter objects.
     */
    private int shrinkArray(VisitorAccepter[] array, int length) {
        int counter = 0;

        // Shift the used objects together.
        for (int index = 0; index < length; index++) {
            VisitorAccepter visitorAccepter = array[index];

            if (usageMarker.isUsed(visitorAccepter)) {
                array[counter++] = visitorAccepter;
            }
        }

        // Clear any remaining array elements.
        if (counter < length) {
            Arrays.fill(array, counter, length, null);
        }

        return counter;
    }
}
